Many organic compounds have enantiomeric isomers which have completely the same physical and chemical properties but differ in physiological activity. This is attributable to the following. In most cases, proteins or glucides per se constituting a living being are composed of only one of the enantiomeric isomers, and for this reason, a difference arising in the manner of acting on the other enantiomeric isomer results in a difference in physiological activity. In particular, in many cases, there are significant differences in medical properties and toxicity between the enantiomeric isomers of the pharmaceuticals, and this problem is recognized as a significant problem in the field of pharmaceuticals. The Ministry of Health, Labour and Welfare of Japan prescribes in the Guideline for the Production of Medicines that “in the case where the drug is a racemi form, it is desirable that studies on the dynamic behaviors of absorption, distribution, metabolism and excretion be made on each enantiomeric isomer”.
Since the enantiomeric isomers have completely the same physical and chemical properties, for example, the physical properties such as a boiling point, a melting point or a solubility, as described above, they cannot be analyzed by ordinary separation means. For this reason, extensive investigations have been made on techniques for analyzing a wide variety of enantiomeric isomers in a simple manner and with a high precision. As a result, an optical resolution method by high performance liquid chromatography (HPLC), in particular, an optical resolution method using an enantiomeric isomer separation column for HPLC has been developed as an analyzing method that meets those requirements. The enantiomeric isomer separation column defined herein uses an asymmetry identifying agent itself or a chiral immobilizing phase having the asymmetry identifying agent supported on a suitable carrier.
As examples of the chiral immobilizing phase, optically active poly(triphenylmethyl methacrylate). (cf., JP-A 57-150432), cellulose and amylose derivatives (cf., JP-A 60-40952, JP-A 60-108751, JP-A 60-142930 and JP-A 63-178101), ovomucoid, which is a protein (JP-A 63-307829), and the like have been developed. It is known that, of the many chiral immobilizing phases for HPLC, a column for enantiomeric isomer separation having the cellulose or amylose derivatives supported on silica gel has a high asymmetry identification ability for a very wide variety of compounds (for example, Okamoto et al., Angew. Chem. Int. Ed., 1998, 37, 1020).
In the case of aiming at analyses such as an optical purity measurement, it has been desired that as many unidentified enantiomeric isomer compounds as possible can be separated by as few kinds as possible of enantiomeric isomer separation columns. As a result, the above-mentioned column for enantiomeric isomer separation having the cellulose or amylose derivatives supported on the silica gel has been accepted as practical separation media.
In recent years, studies on liquid preparative chromatography for optically active substances on an industrial scale in a combination of a chiral immobilizing phase for HPLC and a simulated moving bed method have been developed (Phrarm. Tech. Japan, 12, 43(1996). In such studies, not only analysis, but also preparative separation, namely, chromatographic separation as a production means, are noted.
For that purpose, in order to not only merely perform base line separation, but to improve the productivity of the preparative chromatography and decrease the production cost, it has been demanded to develop a chiral immobilizing phase that enables the further separation of a target compound for the limited, specified preparative separation, that is, has a value of separation coefficient α as high as possible.
On the other hand, a molecular imprinting method is known as a method of specifically identifying the specific target compound. The most popular method in general production methods for a molecular template is that the target compound (guest) and a monomer for performing non-conjugated-bond-type interaction therewith are reacted in a test tube using a crosslinking agent or the like for polymerization, thereby obtaining a polymer compound (host). Further, a method of obtaining a host by mixing the guest and a polymer and subjecting the polymer to a crosslinking reaction in an interaction state is known (for example, G. Wulff et al., Angew. Chem., 1972, 84, 364).
A filler for chromatography obtained by such molecular imprinting has a high identification ability for a guest. However, it is known that such a filler is extremely high in its degree of adsorption for a guest, and as a result, the corresponding elution peak shows a widely extended form. This is not satisfactory in terms of chromatography efficiency. Further, the polymer compound obtained by the molecular imprinting method cannot include a dissolution operation that may decompose a prepared template. For this reason, the polymer compound is prepared into the filler for chromatography by pulverization processing or the like. However, an operation such as classification is complicated, and a particle size is not uniform, resulting in a decrease in chromatography efficiency. For the above reason, the filler for chromatography obtained by the technique using the molecular imprinting method has not been yet put into practical use.
A purpose of the present invention is to provide a process for producing a novel separating agent for separating enantiomeric isomers to obtain a separating agent for separating enantiomeric isomers, which is greatly improved in separation efficiency for objective compounds for separation.
Another purpose of the present invention is to provide a separating agent for separating enantiomeric isomers, which has a greatly improved separation performance for a compound to be separated and can separate compounds that could not conventionally be separated.
Still another purpose of the present invention is to provide an immobilizing phase for chromatography or an immobilizing phase for continuous liquid preparative chromatography, using the separating agent for separating enantiomeric isomers, and a separation method for enantiomeric isomers.